A. Field of the Invention
This invention relates to a method and apparatus for a thin film negative temperature coefficient (NTC) thermistor.
B. Problems in the Art
The current process of making a negative temperature coefficient of resistance thermistor has a number of deficiencies. In the current process, a mixture of metal oxide powders is weighed and mixed with organic materials being added as binders. Once mixed, the mixture is ground and tape casted to turn the metal oxide powder into a thin and flexible tape-like material. These thin tapes of metal oxide materials are then cut into pieces, stacked one on top of each other and pressed. The resulting product at this point of the process is called a raw wafer. The raw wafer is then fired at approximately 1100° C. for nearly seven days. This includes the ramp up and ramp down time to and from that temperature. The aforementioned process is considered to be the preprocessing of the thermistor. After preprocessing, a thick film glass dielectric is sprayed on the top and the bottom of the preprocessed wafer. Then parts are diced to the desired width and broken into strips. Glass dielectric is then sprayed on the edges. The resulting pieces are then cut to a length to obtain the correct and desired resistance values. Termination is then performed on the open edges, that is the edges without glass dielectric, by dipping the edges into platable silver ink. The thermistor is later fired at approximately 650° C. and electroplated with Nickel and tin-lead, or other solder material.
This current process produces a number of problems and deficiencies. One problem is that the process takes too long due to the long time period of firing.
Another problem is that the resistance value is dependent in part upon the physical size of the resulting thermistor.
Another problem is that because of the thickness of the device, the thermistor takes a longer amount of time to heat up than is desirable.
Another problem is the resistance tolerance associated with the thermistor. Because the material composition in a particular thermistor can vary, the resistance varies as well, resulting in a tolerance that is greater than desired.
Thus it is a primary objective of the present invention to provide a negative temperature coefficient of resistance thermistor which improves upon the state of the art.
Yet another objective of the present invention is to provide a thermistor which is predictable.
Another objective of the present invention is to reduce material costs in manufacturing.
Another objective of the present invention is to reduce labor costs associated with manufacturing.
Another objective of the present invention is to make a thermistor with a tighter resistance tolerance.
Another objective of the present invention is to provide a thermistor with reduced manufacturing time required.
Another objective of the present invention is to provide a negative temperature coefficient of resistance thermistor that can be manufactured with thin film techniques.
Another objective of the present invention is to provide a thin film thermistor having the advantage of reduced heating time.
It is another objective of the present invention to provide a negative temperature coefficient thermistor having the advantage of reduced thickness.
It is another objective of the present invention to provide a negative temperature coefficient resistor having increased sensitivity to temperature changes.
These and other objectives, features, or advantages of the present invention will become apparent from the specification and claims.